Acetate filaments of improved resistance to hydrothermal delustering and the process for preparation thereof

ABSTRACT

CELLULOSE ACETATE FILAMENTS HAVING EXCELLENT RESISTANCE TO HYDROTHERMAL DELUSTERING IN HOT WATER OF 110*C. AND ABOVE, GOOD QUALITATIVE REPRODUCIBILITY AND PRACTICALLY SATISFACTORY FIBER STRENGTH, AND PROCESS FOR PRODUCING SUCH FILAMENTS BY USING CELLULOSE ACETATE FLAKES WHICH HAVE BEEN POST-TREATED UNTIL THEIR REFINED PARAMETER AT THE STABILITY OF 0.08% IS REDUCED TO NO HIGHER THAN 80.

United Smtes Patent 3,595,854 Patented July 27, 1971 3,595,854 ACETATEFILAMENTS OF IMPROVED RESIST- AN CE T HY DROTHERMAL DELUSTERING AND THEPROCESS FOR PREPARATION THEREOF Masao Matsuzaki, Matsuyama-shi, Japan,assignor to Teijin Limited, Osaka, Japan No Drawing. Filed Nov. 26,1968, Ser. No. 779,271 Claims priority, application Japan, Nov. 28,1967, 42/ 76,632 Int. Cl. CllSb 3/22 US. Cl. 260-230 3 Claims ABSTRACTOF THE DISCLOSURE Cellulose acetate filaments having excellentresistance to hydrothermal delustering in hot water of 110 C. and above,good qualitative reproducibility and practically satisfactory fiberstrength, and process for producing such filaments by using celluloseacetate flakes which have been post-treated until their refinedparameter at the stability of 0.08% is reduced to no higher than 80.

This invention relates to a process for the preparation of acetatefilaments having excellent resistance to hydrothermal delustering, withgood reproducibility, in which the inherent deficiency of celluloseacetate, filaments, i.e., hydrothermal delustering, is conspicuouslyeliminated without detrimental effect on the filaments favorableproperties such as silk-like hand, luster, clarity of dyed color andpractical strength, etc., and also relates to such improved filaments.The filaments of the invention exhibit no appreciable delusteringphenomenon, which subjected to, for example, a treatment with hot waterof 110 C. under an elevated pressure.

More particularly, the invention relates to a process for thepreparation of acetate filaments of which hydrothermal delusteringproperty is improved, comprising dissolving acetone-soluble cellulosediacetate flakes in a solvent system composed chiefly of acetone, andspinning the solution into acetate filaments, the characteristicfeatures residing in that the flakes are subjected to a heatingposttreatment in a dilute aqueous acid solution until their refinedparameter at the stability of 0.08% is reduced to no higher than 80, andthen removed of the treating liquid by washing, followed by the saiddissolving and spinning steps, and relates also to thus obtainedcellulose acetate filaments.

Cellulose acetate filaments possess such favorable properties assilk-like hand, luster, clarity of dyed color, and

practically valuable tenacity, etc. On the other hand, they tend todeluster in hot water and change to milky White state. Degree of suchdelustering is intimately related to the temperature of hot water. Thatis, up to approximately C., little appreciable delustering takes place,but the delustering is considerable in boiling water. At temperaturesexceeding C., it is markedly advanced, and the filaments turn milkyWhite which is observable with naked eye. Thus, cellulose acetatefilaments which show no appreciable delustering phenomenon in hot waterexceeding 100 C. (under elevated pressure), for example, C. or higher,do not exist, and therefore the elimination of this delusteringphenomenon was considered to be impossible.

Thus delustered filaments exhibits inconveniently remarkableabnormalities in their fiber properties, particularly reduction instrength and increase in elongation. Such tendency is more conspicuousat advanced degree of delustering. Thus this drawback incurs indeedheavy limitations on the utility of cellulose acetate filaments.

For example, recently various mixed or blended weaving techniques areunder development, effectively utilizing both the favorable propertiesof cellulose diacetate such as elegant feeling, clarity of dyed color,etc. and the excellent strength property of synthetic fibers such as ofpolyester. Therefore novel type of cellulose diacetate filaments whichdo not deluster in hot water of the temperatures in the order of 110130C., which are normally employed for dyeing of synthetic fibers, forexample, polyester, have been in urgent demand. That demand, however,has not been met to date, and all the existing cellulose diacetatefilaments completely lose luster under said temperature condition, andtheir color tone is markedly impaired. Furthermore, their favorableproperty such as the fine, elegant feeling also is destroyed.

We engaged in extensive research works in pursuit of cellulose acetatefilaments which exhibit markedly improved resistance to the hydrothermaldelustering without any sign of deterioration in their favorableproperties, in order to meet the above demand. In the course of studieswe discovered that the main cause of hydrothermal delustering ofcellulose acetate filaments is not the forma tion of crazing in thesurface structure of the filaments but of microvoids of the diameters inthe order of 0.02-- 0.5 micron in the filaments, and that the degree ofdelustering advances not with the growth in size of the microvoids, butwith the increase in number thereof. We also found that in celluloseacetate of high acetyl value, the number of such microvoids formed isremarkably less.

Whereas, when we tested the hydrothermal delustering of the filamentsprepared in identical manner from various cellulose acetate flakes ofhigh acetyl value and of same quality, under identical test conditions,the results were entirely unpredictable. That is, the degree ofdelustering of the specimens were very much dispersed. Therefore under ahypothesis that the hydrophilic impurities of cellulose acetate flakessuch as ash content, trace of free acetic acid, etc. may provide thebases or points in the resulting acetate filaments to draw the watermolecules in hot water, and assist the microvoids formation as theycause distortion in dry filament structure, we repeated the identicaltest using cellulose acetate flakes of identical impurities contents.The results were in no way changed.

Generally speaking, cellulose acetate flakes of high acetyl value andlow hydrophilic impurities contents exhibit less tendency fordelustering, compared with those of lower acetyl value of higherhydrophilic impurities contents. From this fact, those factors appear tobe somewhat correlated with the degree of delustering. However, theresults of our experiments, that the degrees of delustering weredispersed as to the specimens in which those factors were identical,indicates that the prediction of delustering phenomenon of celluloseacetate filaments using those factors as the sole norms is impossible.Furthermore, in hot water exceeding 100 C., the filaments weredelustered and became useless for any practical purpose, irrelevantly tothe factors.

We pursued our studies aiming at the development of cellulose acetatefilaments having heretofore unknown excellent resistance to hydrothermaldelustering with good reproducibility. Whereupon we came to know that ifthe conventional stabilizing means of cellulose acetate is applied tothe cellulose acetate flakes as a post-treatment thereof under theconditions heretofore avoided in the stabilizing operation, until therefined parameter at the stability of 0.08% (this term will be preciselydefined later in this specification) is reduced to no more than 80, thecellulose acetate filaments prepared from such flakes exhibit anentirely novel property, i.e., excellent resistance to hydrothermaldelustering in hot Water of 110 C. and above (under elevated pressure),for example, as high as 140 C., and furthermore the sufficient strengthfor practical use.

Conventionally, such means as thorough washing with water and boiling inwater or dilute acid are well known as the stabilizing treatments ofcellulose acetate, in order to completely eliminate the residual freeacid from the precipitated cellulose acetate. Also the treatment withdilute acid and aqueous sodium chlorite solution is known as a bleachingand stabilizing means of cellulose acetate.

On the other hand, it has been the accepted practice among the expertsto complete this dilute acid treatment within a shortest periodpossible, normally about l-2 hours. Because, such dilute acid treatment,if continued for a long time, causes non-uniform. saponificationdecomposition of acetic acid radicals of cellulose acetate and degradesthe solubility thereof to acetone. And, the decrease in the acety valuetends to aggravate the hydrothermal delustering of cellulose acetatefilaments as aforesaid. Therefore, the dilute acid treatment for a longperiod which invites decrease of acetyl value appears to beobjectionable also in this respect.

Whereas, quite surprisingly it is found that when the treatment iscontinued for a much longer period than that conventionally employed forstabilizing purpose, i.e. until the aforesaid new parameter issatisfied, the so treated flakes provide novel type of cellulose acetatefilaments having high resistance to hydrothermal delustering asdescribed in the foregoing. It is furthermore discovered that thefilaments of the strength quite satisfactory for practical purposes canbe obtained by suitably selecting the acetyl value of the flakes beforethe dilute acid treatment.

Again, the cellulose acetate filaments prepared from the flakes whichhave been so post-treated until the specified parameter is satisfied,exhibit always excellent resistance to hydrothermal delustering andfully satisfy 4 the reproducibility of the high quality. Whereas, themeasured values of the said parameter of commercially availablecellulose acetate flakes are no less than 150, normally above 200.

Accordingly, the object of the invention is to provide novel celluloseacetate filaments having excellent resistance to hydrothermaldelustering, good qualitative reproducibilty and practicallysatisfactory fiber strength, and a process for the preparation of suchfilaments.

Still many other objects and advantages of this invention will becomeapparent from the following descriptions.

In the invention, cellulose diacetate flakes (which may be hereafterreferred to as acetate flakes) include all forms of dry cellulosediacetate used as the spinning material, for example, powder, granule,pellet, foil, short staple, etc.

According to the invention, the acetate flakes are subjected to aheating post-treatment in dilute aqueous acid solution, for example,dilute aqueous solution of a mineral acid such as sulfuric, nitric,phosphoric, and hydrochloric acids, or of a lower fatty acid such asacetic acid. It is permissible to perform the post-treatment in theconcurrent presence of similarly dilute aqueous solution of bleachingagent, such as of sodium hypochlorite, hydrogen peroxide, potassiumpermanganate, etc. Or, the flakes may be treated with such bleaching orreduction bleaching agent, after the specified dilute acidpost-treatment.

The concentration of acid in the dilute aqueous solution for the heatingpost-treatment may range from approximately 0.l% to approximately0.001%, in case mineral acids are employed. The concentration can besuitably varied, depending on the type of acid, shape of flakes, heatingtemperature, etc. The preferred concentration is normally aroundODS-0.005%, inter alia, approximately 0.040.0l%. Also when lower fattyacid is employed, it may range approximately 100.5%, preferably 60.8%,inter alia, in the order of 4-l%.

Normally the heating temperature ranges about 200 C. Preferred range isabout 180 C., inter alia, in the order of 90-160 C. The temperature issuitably selected depending on such factors as heating time, type andconcentration of acid, shape of flakes, etc.

The treatment can be performed batchwise or continuously. For instance,the flakes may be suspended in a tank filled with the aqueous acidsolution, to be heattreated. Or heated aqueous acid solution may becaused to flow down through a column packed with the flakes. Also theflakes continuously supplied from the top portion of a treating columnmay be countercurrently contacted with the aqueous acid solutionsupplied from bottom portion of the column as an upward flow. Or,heated, dilute aqueous acid solution may be sprayed on the acetateflakes which are being transferred on a movable belt. in short anyoptional method can be employed, so far as the aqueous acid solution andthe solid flakes can intimately and uniformly contact with each other.

The treatment can be performed under either atmospheric or elevatedpressure. Also if desired, it is permissible to employ a slightlyreduced pressure condition under which the aforesaid heating temperaturecan be maintained.

Duration of this post-treatment is suitably varied or selected accordingto such factors as type and concentration of the acid, shape and amountof the flakes, treating system, pressure condition, etc., but in allcases it must be long enough to satisfy the aforesaid parameter.

Any treatment not satisfying the parameter is not within the scope ofsubject process. The products fail to show the resistance tohydrothermal delustering at temperatures exceeding C., and qualitativereproducibility is impaired.

In the present invention, the acetate flakes must be post-treated, untiltheir refined parameter at the stability of 0.08% is reduced to no morethan 80.

After the post-treatment, the flakes are thoroughly washed to remove thetreating liquid remaining thereon. Warm water shows better washingefficiency than cold water. For example, warm water of about 4095 C. canbe advantageously used. Or a dilute alkaline aqueous solution can beused for the same purpose.

Thus treated acetate flakes are normally dried, and dissolved in asolvent system composed chiefly of acetone by the means known per se.The cellulose acetate filaments spun therefrom exhibit no appreciabledelustering in hot water of above 100 C., for example, 110-150 C. (underelevated pressure). Such cellulose acetate filaments are never beforeproduced, although very much wished for.

The filaments can be imparted with strength suflicient for practicalpurposes. In the present invention, it is particularly advantageous anddesirable for imparting the resistance to hydrothermal delustering athigh temperatures with good reproducibility to the filaments, that therelation expressed by the equation below is satisfied by the watercontent and acetyl value of the cellulose acetate dope to beprecipitated to provide the material flakes, the dope having beenalready acetylated and aged:

Water content of dope (wt. percent =(213-3.5 acety1 value) :3.0

In the present invention, that the refined parameter at the stability of0.08% is no more than 80 signifies that the numeral value measured andcalculated by the following method is no more than 80.

METHOD OF MEASUREMENT AND CALCULATION OF REFINED PARAMETER (I) Thesample flakes are pulverized and 2 g. of the resulting powder accuratelyweighed with chemical balance is placed in a heat-resistant hard glass(Pyrex by the trade name) test tube. After addition of further 2 cc. ofpure water, the test tube is closed airtightly with a rubber plug whichhas been thoroughly cleaned in boiling pure water. While maintainingthus sealed state, the test tube is immersed in boiling water to beheated for 7 hours. Then the content is separated into the solid sampleand solution by means of quantitative filter paper, and the solidcomponent is washed with 150 cc. of boiling pure water. The foregoingsolution and washing are combined, and quickly neutralization titratedwith 0.01 N aqueous caustic soda solution, using phenol-phthalein as theindicator.

In that stage, the water obtained through the identical procedures asabove except the addition of the sample is omitted is similarly quicklyneutralization titrated by way of a blank test, and the first titrationvalue is corrected by subtracting the blank titration value therefrom.

From thus corrected titration value, the percentile acetic acid content(A) per sample weight is calculated.

Separately, g. of the same sample is precisely weighed and is immersedin 100 cc. of pure water at room temperature for 3 hours and filtered.Then the solid component of the sample is washed with 50 cc. of purewater, and the filtrate and washing are combined. The liquid is alsoneutralization titrated with 0.01 N aqueous caustic soda solution, usingphenolphthalein as the indicator. Separately a blank test is conducted.The percentile acetic acid content (B) per sample weight is thencalculated.

The numeral value obtained by subtracting (B) from (A) is calledstability in this specification.

(II) Separately, 10 g. of the same sample is put in a porcelaincrucible, and first calcined by pre-heating, followed by burning in 800C. electric oven. The solid component is dissolved in hydrochloric acidin accordance with the accepted practice, and using Eriochrome Black-Tindicator, its calcium and magnesium contents are measured with EDTA(ethylenediaminetetraacetic acid 2-sodium). The result (converted tocalcium) per sample weight is indicated by ppm. unit (which is referredto as alkalinity in this specification).

(III) Several groups of each g. of sample flakes are prepared, which areimmersed in each 2 liters of water of various hardness (IIS K-0101),which has been prepared by adding calcium acetate to pure water, for 24hours at room temperature, and thereafter withdrawn and dried. Thusobtained plural groups of dry samples are each determined of thestability (Y) and alkalinity (X) according to the procedures (I) and(II) above.

With reference to the perpendicularly crossing co-ordinates in which theordinate denotes stability and abscissa denotes alkalinity, the setvalues of the above samples are plotted, and the points are connectedwith a smooth curve. Then the reading of alkalinity corresponding to theintersection of this curve with the level of 0.08% stability isdetermined. This reading (p.p.m.) is the refined parameter (SP) at thestability of 0.08%.

The hardness of the water for immersing the flakes can be suitablyselected to secure the intersection of the said curve with the 0.08%stability level. That is, when the stability of the sample flakes isabove the level of 0.0 8%, plural types of water having hardnessesexceeding 2.5 times of the alkalinity corresponding to that stabilityare selected. And, if the stability of the sample flakes is below thelevel of 0.08%, the hardnesses of less than 2.5 times the correspondingalkalinity are selected.

The curve showing the correlation of stability with alkalinity of thesample obtained as described in the foregoing resembles a hyperbola forwhich the axis of abscissa and a straight line perpendicularly crossingtherewith are the asymptates. The location of the straight lineperpendicularly intersecting with the axis of abscissa varies, dependingon the composition of acetate flakes employed.

It is not yet perfectly clear why the SP value of the acetate flakes inaccordance with the present invention provides a highly reliable,excellent parameter for prediction of hydrothermal delustering andqualitative reproducibility of the cellulose acetate filaments preparedfrom the same flakes. However, the filaments made from the flakessatisfying this parameter exhibit excellent resistance to hydrothermaldelustering and high qualitative reproducibility. More specifically, thefilaments show the degree of delustering (Whcih will be defined later)of no more than grade 1.5 in hot water of 110 C., for example, grade 0.3or 0.2 which means substantially no appreciable delustering.

DEGREE OF HYDROTHERMAL DELUSTERING AT 110 C.

The sample cellulose acetate filaments of 100 deniers/ 25 filaments aremechanically wound onto a frame into six layers, over a width of 3 cm.without gaps. The frame is then immersed in hot water in an autoclavewherein the temperature is controlled to 95 C. The autoclave isimmediately closed airtightly, and inside temperature thereof is raisedto 110 C. during the following 30 minutes. After an additional hour ofthe immersion at that temperature, the frame is withdrawn and air-driedat room temperature for 30 minutes. Subsequently the filaments are driedin a constant temperature drying oven of C. The degree of delustering ofthe filaments is then graded in comparison with the standard samples.

When identical test is performed except the temperature is raised to 140C. instead of C, the result is referred to as the degree of hydrothermaldelustering at C. Similarly, when the testing temperature is 100 C., theresult is the degree of hydrothermal delustering at 100 C.

The standard samples are prepared to have successively increased degreeof delustering with rise in the numerical grade, starting from the gradezero denoting the status of filaments before the hydrothermal treatment,to enable 8 Degree of delustering: Factor Per one sample exceeding grade1.5 to grade functional determination of the grade. .At the delustering3.0 "a- +0.3 grade 5, the filaments are substantially milky white. -AsPer one sample exceeding grade 3.0 to gra e referential values, thecorresponding whiteness values (L- 5 5.0 +0.8 values) measured with thecolor-difference meter of Nip- Per one sample exceeding grade 5.0 P0iDeIlShOkll Kogyo w which is designed to measure Hereinafter the severalembodiments of the subject the tristimulus values of color, are given inthe below. process will be explained with refergnce to ki exam- When thesample filaments are photo-irradiated at the P1es angle of 45 to theadvancing direction of the wound fila- Examples 1 4 controls 1 2 mentson the frame and L-values of the reflected light are determined, thecorrespondence become as in the table o .h ndred (100) parts ofcellulose Were pre-treated below. with 50 parts of acetic acid, andsubjected to an acetylation reaction with 350 parts of acetic anhydride,400 parts Hydrothermal delustering 15 of methylene chloride, and 1 partof sulfuric acid as the grade Lvalue 1 catalyst, under stirring at atemperature not higher than 0 C, After the reaction system became a homg 35 solution and acquired the predetermined viscosity, 80 1.0 43 partsf water and 5 parts of sulfuric acid were added to 48 20 perform theaging reaction at temperatures below 50 C. 2.5 61 When the acetyl valuereached 55.0%, the Sulfuric aci 30 66 was neutralized with equivalentamount of sodium car- 4.0 7 bonate dissolved in parts of Water, 10terminate h 5.0 78 reaction. 1 Measured with color difference m t r, 25Thereafter the reaction mixture was heated so that the most of methylenechloride in the dope was removed by The cellulose acetate filamentsprepared in accordance evaporation The remaining system i i d i with thepresent invention, that is, the filaments prepared 18% aqueous acetic idsolution. from the cellulose diacetate flakes which have been post- Thprecipitated flake were washed with water. A treated until their refinedparameter at 0.08% stability is 30 ti th f was d i d on-treated flakeand the reduced 110 more than 80, y dissolving the flakes in a rest wasdivided. The specimens were boiled in 0.02% solvent system composedchiefly of acetone and spinning aqueous sulfuric acid solution, each 2,4, 10, 20 and th am n accordance w accepted Practice, P088685 30 hours.Then the sulfuric acid was completely washed heretofore unknown highresistance to hydrothermal demi fro th specimens with water. Then SPparameter of lustering, such as the degree of hydrothermal delustering35 each specimen was measured. They were subsequently at 110 C. of grade1.5 or less. Also the grade shows exdissolved in acetone and spun in theaccepted manner. cellent qualitative reproducibility of no less than Asto the resultant filaments, degrees of hydrthermal denormally Thequalitative reproducibility is callustering at 100 C., C., and C., andqualitaculated as follows: tive reproducibility were measured, with theresults as The above-described hydrothermal delustering test at given inTable 1 below.

TABLE 1 SP at Degree of hydrothermal Qualitative 0.08% delustering(grade) at reproducstabllity, ibility, No. Flakes (p.p.m) 100 C. 110 0.140 0. percent Control 1 Untreated flakes 215 3. 0 4. 0 5. 0 50 Control2 Flakes treated (2 hours) 1. 5 2. 6 4. 0 30 Example 1 Flakes treated (4hours)... 91 0 1. 5 3. 0 +95 Example 2. Flakes treated (10 hours) 78 00. 5 0. 6 +100 Example 3 Flakes treated (20 hours) 30 O 0.3 0. 4 +100Example 4 Flakes treated (30 hours) 18 0 0 0. 2 +100 110 C. is given to24 filament samples taken from the filaments made from identical flakes.The number of samples whose delustering grade exceeded 1.5 is counted,and the result plus the below-specified factor, P, is used as the basefor calculating the qualitative reproducibility in accordance with theequation below:

Qualitative reproducibility (percent) 24 100 Examples 5-8, controls 3-9TABLE 2 Post-treatment of flakes SP at 0.08% Hydrothermal delusteringdegree at 100 0. 110 0. 140 0.

Acid coneen- Treating tration, time percent (his) Treating temp. 0.)

Dope, percent Water Acetyl content value Acid used pr%sure) Control 4IExample 7 Control 5 Control 6 Control 7 Control 8. r Control 9 i Thebefore treatment and after treatment respectively mean before and aiterthe hot Water treatment of a skein yarn in the same manner as themeasurement of hydrothermal delustering degree at 110 C. The strength isa dry strfingth both before and after treatment.

5 Commercial product (acety1valuo=54.9%; degree of polymerization-=182.

4 Under concurrent use of aqueous solution of sodium hypochlorlto.

I claim:

1. A process for the preparation of cellulose diacetate filaments whichhave a degree of hydrothermal delustcring at 110 C. of not more thangrade 1.5 and a qualitative 5 reproducibility of 97-l00% whichcomprises:

(a) heat-treating cellulose acetate flakes in a dilute aqueous acidsolution, wherein the acid is selected from sulfuric, nitric,phosphoric, hydrochloric and acetic acids, until the refined parameterat a stability 10 of 0.08% is reduced to no greater than 80; said heattreatment being conducted at a temperature ranging from the boilingpoint of said solution to 200 C.

(b) Washing said flakes to remove said aqueous acid solution therefrom;

1 (c) dissolving the flakes free of said aqueous acid solution in asolvent system consisting essentially of acctone; and

(d) thereafter spinning the solution of (c) into filaments.

2. The process of claim 1 wherein the concentration of acid in thedilute aqueous acid solution is 0.l-0.001% in the case of sulfuric,nitric, hydrochloric and phosphoric acids and 0.86% in the case ofacetic acid.

3. The process set forth in claim 1, in which the flakes are thoseobtained by precipitating the aged dope of cellulose diacctate of whichWater content and acetyl value satisfy the relation of:

Water content of dope =(213-3.5 acetyl value)i3.0

References Cited UNITED STATES PATENTS 1,286,172 11/1918 Dreyfus 260-2301,824,877 9/1931 Dreyfus et al 260230 2,203,699 6/1940 Seymour et a1. 26023 0 3,505,313 4/1970 Kato 260-230 FOREIGN PATENTS 68,001 9/1911Switzerland 260--230 298,819 10/1928 Great Britain 260230 299,326 3/1930Great Britain 260-230 312,232 1930 Great Britain 260-230 DONALD E.CZAJA, Primary Examiner R. W. GRIFFIN, Assistant Examiner US. Cl. X.R.l06---196, 198

